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  • 學位論文

加速碳酸化對轉爐石中含鈣物種轉化反應之影響

The effect of accelerated carbonation on the calcium species transformation of BOF slag

指導教授 : 柯明賢
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摘要


本研究以三種粒徑(3.5~7mm、7~15mm及15~25mm)之轉爐石於不同反應溫度、二氧化碳含率、水氣含率及反應時間等操作參數下進行加速碳酸化之研究,探討加速碳酸化對轉爐石特性之影響,以評析轉爐石加速碳酸化之可行性、最適操作參數及反應行為。由研究結果可以發現,轉爐石之主要化學組成為Ca、Fe、Mg、Si、Al等氧化物,其中以鈣的成分居多且亦存在f-CaO約3.94 %~6.28 %,顯示轉爐石應具有碳酸化之潛勢。而轉爐石加速碳酸化於最適操作條件(200℃、40%CO2及60%H2O)下進行加速碳酸化,三種粒徑之轉爐石其pH值分別從12.3、12.0及11.9下降至10.8、10.5及10.4,三種粒徑之轉爐石其熱重損失則分別從1.28 %、1.09 %及0.79 %增加至1.72 %、1.38 %及1.57 %。由OM礦物相及SEM顯微結構的觀察中則發現轉爐石表層應有碳酸鈣成份礦物的生成,而由XRD晶相繞射及FTIR光譜則分別亦可以發現轉爐石經加速碳酸化後表層有Caclite晶相及碳酸根特性吸收峰存在。 而由不同反應時間進行轉爐石加速碳酸化之研究結果可以發現,轉爐石表層之碳酸鈣晶粒大小及碳酸化厚度隨著反應時間增加而增加,且表層碳酸鈣之礦物結構則隨著反應時間由針織結構的霰石轉化為立方體結構的方解石。由XRD繞射分析結果可以發現,轉爐石表層中Calcite晶相繞射峰強度隨著反應時間增加而增加,但Portlandite與Lime的晶相繞射峰強度則隨著反應時間增加而減少。由FTIR圖譜中可以發現,轉爐石於不論經3、5、24小時加速碳酸化後其表層均存在有碳酸根的特性吸收峰,但Si-O的特性吸收峰則由943 cm-1及983 cm-1往高波數移動。由f-CaO與Ca2SiO4的化學組成分析及熱重分析結果可以發現,加速碳酸化之轉爐石表層所形成的碳酸鈣主要應來自其所含f-CaO及Ca2SiO4之鈣系物種的轉化。 另外,由毒性溶出特性試驗得知加速碳酸化後轉爐石之重金屬Cu、Cr、Pb、Ni及Zn均有明顯下降的趨勢,而由桶槽溶出試驗得知加速碳酸化後轉爐石之重金屬Cr、Pb及Ni之溶出量亦均有明顯下降趨勢。綜合以上研究結果顯示,轉爐石表層之氧化鈣及矽酸鈣於加速碳酸化過程中,應會先行發生水化反應形成Ca(OH)2及CSH膠體 ,而Ca(OH)2及CSH膠體再以液相碳酸化反應形成碳酸鈣,直到碳酸鈣佈滿轉爐石表層之孔隙,碳酸化反應即趨於平衡。而轉爐石進行加速碳酸化於其表層所形成之碳酸鈣,具有降低轉爐石高鹼性及穩定重金屬之功效,可提昇轉爐石資源化利用之價值,並兼具二氧化碳減量之效果。

並列摘要


In this study, the effects of accelerated carbonation on the chemical properties, mineral morphologies and microstructures of BOF slag under various accelerated carbonation parameters are evaluated. Under optimum accelerated carbonation parameters, the results indicate that particle size 3.5 to 7mm, 7 to 15mm and 15 to 25mm of BOF slags individually lowered their pH values from 12.3, 12.0 and 11.9 to 10.8, 10.5 and 10.4. Besides, thermal weight loss of BOF slags for particle size 3.5 to 7mm, 7 to 15mm and 15 to 25mm individually increased from 1.28 %, 1.09 % and 0.79 % to 1.72%, 1.38% and 1.57%. The mineral morpgology micrographs and SEM micrographs of accelerated carbonation BOF slags show that the surface of BOF slag was feasible to form calcium carbonate. The XRD patterns of accelerated carbonation BOF slags show that there were calcite on the surface of BOF slag and the spectra of FTIR of accelerated carbonation BOF slags indicate that there were CO32- function groups presenting on surface of carbonated accelerated carbonation BOF slags. Based on the investigation of chemical properties, mineral morphologies and microstructures of accelerated carbonation BOF slags on different reaction time, the results show that the grain size and thickness of calcium carbonate and the diffraction peak intensity of calcite on accelerated carbonation BOF slag surface increase with the reaction time. The calcium carbonate of BOF slag surface was formed by the reaction of Ca(OH)2 and CHS gels produced from the hydration of the f-CaO and Ca2SiO4 with carbon dioxide through aqueous carbonation. Furthermore, the results in accordance with TCLP and Tank Leaching tests indicate that the leaching concentration of Cu, Cr, Pb,Ni and Zn in accelerated carbonation BOF slag was obviously decreased. Based on the above results, accelerated carbonation of BOF slag not only reduces high alkalinity of BOF slag and leachability of heavy metals in BOF slag, but also promotes the utilization of BOF slag and reaches the reduction of carbon dioxide.

參考文獻


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